1. Field of the Invention
The present invention relates to a communication control server, a communication terminal and a communication control method, and in particular to a communication control server for providing a SIP session using a packet connection communication channel in a mobile communication network, a communication terminal and a communication control method.
2. Description of the Related Art
Realization of PoC (Push-to-Talk over Cellular) communication is scheduled which makes it possible to use a mobile terminal device, such as a cellular phone, like a transceiver and realize communication among multiple users in a group only by touching a button.
PoC communication is quick communication means to be used between two users or in a group, and it is possible to use a terminal device like a transceiver in the PoC communication. The operation for starting conversation is performed not by pressing dial buttons but by simply pressing a particular button.
Currently, PoC communication is standardized (OMA-RD_PoC-V1—0-20041115-C) based on the PoC Charter (OMA-CHARTER_PoC-V—0-20031014-A) by the OMA (Open Mobile Alliance), an industry organization which promotes standardization of mobile application techniques.
In order to perform PoC communication, it is the premise that a communication channel has been already formed. Following a Registration message and an INVITE message by SIP (Session Initiation Protocol), acquisition of the right to speak by RTP (Real Time Protocol) is performed.
Description will be made on processings from starting PoC communication when a communication channel has not been formed yet to ending the PoC communication, with reference to FIGS. 5 to 10. In the figures, there are shown three terminals TA, TB and TC which are provided with a PoC communication function and a PoC server 100 which controls a PoC communication service.
(Formation of a Communication Channel)
In order to perform PoC communication, it is necessary that a communication channel have been formed as a premise. To form a communication channel, communication channel establishment request signals 50A, 50B and 50C are sent by the respective terminals to the PoC server 100. Thereby, receiving the communication channel establishment request signals 50A, 50B and 50C, the PoC server 100 forms communications channels 51A, 51B and 51C between the respective terminals and itself, as shown in FIG. 6. These communication channels 51A, 51B and 51C are communication channels enabling packet communication, such as a GPRS (General Packet Radio Service) network and a WLAN (Wireless Local Area Network). The PoC server performs position registration processing and the like for the terminals against a subscriber information management server (Home Location Register Server) 200.
(Registration Processing and Invitation Processing)
After the communication channels 51A, 51B and 51C are formed by the above processing, Registration processing is performed. In this example, the Registration processing is performed by the terminal TA of a user A, and a PoC conversation group consisted of the three users A, B and C is specified. In the Registration processing, REGISTER messages 52A, 52B and 52C are sent by the terminal TA of the user A, the terminal TB of the user B and the terminal TC of the user C, respectively. When 200 Ok signals 54A, 54B and 54C are sent after response signals 53A, 53B and 53C from the PoC server to the sent REGISTER message are received, respectively, the Registration processing is completed.
After the Registration processing, the process proceeds to Invitation processing. In the Invitation processing, an INVITE message 55A is sent from the terminal TA of the user A to the terminal TB of the user B and the terminal TC of the user C in the same PoC conversation group, as shown in FIG. 7. This INVITE message includes destination information (information for identifying the terminal TB of the user B and the terminal TC of the user C), transmission source information (information for identifying the terminal TA of the user A), a call identifier (such as a Call-ID), a header portion configured by a transmission route and the like, and a body portion configured by detailed information about the medium (classification whether voice or picture, band and the like).
If the terminals TB and TC of the user B and the user C are set to an automatic mode when they receive the INVITE messages 55B and 55C sent via the PoC server 100, then 200 OK signals 56B and 56C are automatically sent, and PoC communication is enabled. On the other hand, if the terminals TB and TC are set to a manual mode, then a 180 ringing signal is automatically sent first (not shown). Furthermore, by performing an operation such as pressing a button, the 200 OK signals 56B and 56C are outputted, and thereby, PoC communication is enabled.
When, while only the terminal TA of the user A and the terminal TB of the user B are performing PoC communication with each other, an operation such as pressing a button is performed on the terminal TC of the user C in the same PoC conversation group, a 200 OK signal is outputted, and PoC communication by the three users A, B and C is enabled. That is, any member in the same PoC conversation group can join PoC communication later by performing an operation such as pressing a button.
In order to disconnect PoC communication, a BYE message is sent from a terminal to the PoC server. Thereby, the terminal leaves the PoC conversation group which it has joined.
The above processing is performed in accordance with SIP (Session Initiation Protocol) provided in the specification RFC3261 by the IETF (Internet Engineering Task Force).
(Acquisition of the Right to Speak)
In PoC communication, a user cannot speak without acquiring the right to speak. That is, a user can be a speaker only when he has the right to speak. He is a listener when he does not have the right to speak.
In order to acquire the right to speak when PoC communication is being performed, it is necessary to send and receive signals in accordance with RTP (Real-time Transport Protocol) and send a Floor Request signal. Here, as shown in FIG. 8, a floor request signal 57A is sent from the terminal TA of the user A. If the PoC server which has received the floor request signal 57A permits the right to speak, it returns a Floor Grant signal 58A to the terminal TA of the user A. The floor grant signal 58A includes identification information about the terminal to which the right to speak is permitted, information indicating the time of permission, and the like.
On the other hand, if the PoC server which has received the floor request signal 57A does not permit the right to speak, it returns a Floor Deny signal 59A, as shown in FIG. 9. This floor deny signal 59A includes identification information about the terminal to which the right to speak is not permitted, identification information about the terminal which currently has the right to speak, information about the time of permission, and the like.
By making a speech while pressing a button, in the terminal which has the right to speak, the voice is sent to other terminals in the same PoC conversation group as packet data, and it is possible to speak in the group. The right to speak is held while the button is pressed. If the finger leaves the button and stops pressing it, the right to speak is lost. In this case, when pressing the button is stopped, a Floor Release signal 60A is sent from the terminal to the PoC server as shown in FIG. 10, and a state is caused in which no terminal has the right to speak (Floor Idle).
In addition to releasing the right to speak by releasing a button from the condition of being pressed as described above, the right to speak may be released by time-out of a timer.
The protocol for performing the PoC communication described above has a hierarchical structure. That is, as shown in FIG. 11, the protocol has a structure in which RTP is located above a communication channel, and SIP is located above RTP.
As described above, in PoC communication, SIP communication after establishment of a communication channel is specified. Therefore, in the case where a communication channel has not been established, Registration processing is performed after establishing a communication channel on the originating side, and after that, SIP transmission processing such as the Invitation processing is performed. Then, if a communication channel on the destination side has not been established, it is necessary, as the processing on the destination side, to establish a communication channel by Push using a control signal, then perform the Registration processing, and then continue SIP call processing.
That is, in the case where the terminal TA performs the INVITE processing against the terminal TC, a connection request S201 sent from the terminal TA is sent to the PoC sever 100 via an SGSN (Serving GPRS Support Node) and a GGSN (Gateway GPRS Support Node), as shown in FIG. 12. After a response S202 to the connection request is returned to the terminal TA via the GGSN and the SGSN, Registration processing S203 is performed.
After that, an INVITE message S204 is sent from the terminal TA. In this INVITE message S204, the name of the member or group to perform PoC communication is specified as PoC incoming call information.
Receiving this INVITE message S204, the PoC server 100 starts destination user call processing against the terminal TC which is a destination user (S205). Thereby, as an option function, communication channel establishment processing by SMS Push, which is an operation for sending and receiving a short message, is performed if the Registration processing on the destination user side has not been performed yet (S206); Then, Registration processing S207 is performed for the terminal TC, and an INVITE message S208 is sent to the terminal TC after the Registration processing S207 is completed.
Receiving the INVITE message, the terminal TC sends a 200 Ok signal S209. By this 200 Ok signal S209 being sent to the terminal TA, PoC U-Plane (User Plane) is established between the terminal TA and the terminal TC (S210).
An SGSN is one of nodes constituting a packet network, which is provided to connect to a wireless access network in a GPRS environment. A GGSN is one of nodes constituting a packet network, which is to be connected to an ISP (Internet Service Provider) or company network provided to connect to the Internet in a GPRS environment.
As described above, since it is necessary to perform the Registration processing after establishing a communication channel, there is a disadvantage that it takes a lot of time before communication starts if a communication channel on the destination side has not been established, and the convenience of users is decreased.
The present invention has been made to solve the above problem of the conventional technique, and its object is to provide a communication control server capable of, in the case where a communication channel on the destination side has not been established, shortening the time required before communication starts and preventing the convenience of users from being decreased, a communication terminal and a communication control method.